It is well known by those skilled in the art that many image forming apparatuses utilize fusing mechanisms (“fusers”) to bond toner, ink or other image substances to pages receiving reproduced images. Fusers often function at an effective operating temperature needed for proper bonding of the image substance to the target page. If the fuser temperature is too low, the bond may be inadequate, possibly leading to smudging when the page is touched. With each fused page is a drop in the fuser temperature and the need for the fuser to recover to the appropriate temperature before the next page should be processed.
It is also well understood that different printing stock may require a longer fusing time (“dwell time”) than others. Thus the appropriate dwell time for a particular stock is often directly proportional to metrics such as the stock thickness, and the amount and type of coating on the stock surface.
High speed digital copying machines for processing large print jobs are capable of copying books and other documents using mixed stock. For example, several pages of a pamphlet, book, etc. may be printed on “thin” stock making up the body of the book, while the book cover is typically printed on heavier stock requiring a longer dwell time. The typical prior art approach to printing a mixed stock print job is to print the entire job using the slower dwell time required by the heavier stock. For example, a print job using low weight paper or stock (often measured in gsm—“grams per square meter” or pounds per 500 sheets) might have a productivity of 66.6 prints per minute (PPM), while a print job using heavy stock might need to have a 50 percent reduction in the productivity at 33.3 PPM. So that all of the papers are properly fused, the entire print job is processed at 33.3 PPM.
As a further illustration, the prior art approach to print a seven-page print job such as a pamphlet with 5 regular or lightweight stock pages for the body and 2 heavyweight stock pages for the cover pages might reduce the productivity for the entire job to 33.3 PPM to accommodate the heavy cover stock, rather than a productivity (e.g., 66.6 PPM) closer to that available if just the lightweight stock were used.
One prior art approach is described by U.S. Pat. No. 6,160,974 issued to Takahiro Yoshikawa, et al. In the Yoshikawa patent an image forming apparatus such as a conventional copying machine allows a user to choose an “increased interval mode” for processing stock from a particular paper bin or paper tray when the bin or tray contains heavyweight or other paper requiring extra fusing. In other words, the interval between sheets to be processed is standard for all pages, unless the paper emanates from a paper bin which the user has designated for the Copies Per Minute Down Mode, in which case the interval is increased between pages to give the fusing unit extra time to return to the target operating temperature after a thick page has been processed.
In an alternate mode of the Yoshikawa patent approach, the sheet interval is increased during a print cycle when the temperature of the fusing unit drops below a threshold.
What is desirable is a reproduction device that automatically determines the fuser dwell time according to the stock required in the print job without the user having to specify particular paper trays or bins for increased dwell times. It is also desirable to carry out the above aspirations for stored print jobs that are expected to be processed at high rates using the likes of high speed digital printers.